Print to the console: console.log('Hi')
Declare a changeable variable: let x = 5;
Declare a constant: const PI = 3.14;
Old way to declare a variable: var x = 5;
Single-line comment: // comment
Strict equality: a === b
Strict inequality: a !== b
Logical and: a && b
Logical or: a || b
Logical not: !a
Remainder: 7 % 2
Exponent: 2 ** 3
Increment: i++
If statement: if (x > 3) { }
Else if: else if (x === 3) { }
Ternary operator: cond ? a : b
Switch statement: switch (x) { case 1: break; }
For loop: for (let i = 0; i < 5; i++) { }
For...of loop: for (const item of arr) { }
For...in loop: for (const key in obj) { }
While loop: while (x < 10) { }
Function declaration: function add(a, b) { return a + b; }
Arrow function: const add = (a, b) => a + b;
Anonymous function: function () { }
Make an array: const arr = [1, 2, 3];
Add to end of array: arr.push(4)
Remove last item: arr.pop()
Add to start: arr.unshift(0)
Remove first item: arr.shift()
Array length: arr.length
Loop over each item: arr.forEach(x => ...)
Transform every item: arr.map(x => x * 2)
Keep items that pass a test: arr.filter(x => x > 2)
Combine into one value: arr.reduce((sum, x) => sum + x, 0)
Find first match: arr.find(x => x > 2)
Does the array include a value?: arr.includes(3)
Sort an array (numbers): arr.sort((a, b) => a - b)
Join array into a string: arr.join(', ')
Make an object: const o = { name: 'Sam', age: 9 };
Read an object property: o.name or o['name']
Get keys of an object: Object.keys(o)
Template literal: `Hello ${name}`
String length: s.length
String uppercase: s.toUpperCase()
Split a string: s.split(' ')
Convert to number: Number('5') or parseInt('5')
Check not a number: isNaN(x)
Random number 0 to 1: Math.random()
Round down: Math.floor(3.7)
Round: Math.round(3.5)
Absolute value: Math.abs(-3)
Larger of values: Math.max(1, 5)
Undefined: A variable that has not been given a value
Null: An intentional empty value
typeof operator: typeof x
Select an element by ID: document.getElementById('id')
Select with a CSS selector: document.querySelector('.cls')
Change text of an element: el.textContent = 'Hi'
Change style: el.style.color = 'red'
Add a class: el.classList.add('on')
Listen for a click: el.addEventListener('click', fn)
Wait before running code: setTimeout(fn, 1000)
Repeat code over time: setInterval(fn, 1000)
Fetch data from a URL: fetch(url)
Parse JSON text: JSON.parse(text)
Convert to JSON text: JSON.stringify(obj)
Promise: An object for a value that will be available later
async / await: Syntax for writing asynchronous code that reads in order
Try/catch: try { } catch (e) { }
Class definition: class Dog { constructor(name) { this.name = name; } }
this keyword: Refers to the current object
Import a module: import x from './x.js';
Export a function: export function f() { }
Spread operator: [...arr]
Destructuring: const { a, b } = obj;
JavaScript's creator: Brendan Eich, in 1995
Is JavaScript the same as Java?: No, they are different languages

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